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Partial flow filters (PFF) are devices that can capture particulate matter (PM) for a period of time sufficient for its catalytic oxidation. The filter consists of alternating layers of corrugated metal foil and porous sintered metal fleece which captures the particulates. The captured particles are then re-generated passively by nitrogen dioxide (NO2) produced by the oxidation of NO on a diesel oxidation catalyst (DOC) placed before the filter. The filter's robust design and the ability to operate without any maintenance, i.e. no vehicle downtime, have led to an increasing demand for both heavy duty (HD) and light duty (LD) retrofit applications worldwide. Unlike diesel particulate filter (DPF), the PFF will not plug once filled with soot to its maximum capacity in the absence of passive regeneration (low load and low exhaust temperature conditions). Instead, the PM conversion efficiency will gradually decrease, allowing PM emissions to pass through.